Mexico will hope to kill off Iran's World Cup hopes at the first hurdle on Sunday as the world number four begin their campaign to make it past the quarter-finals for the first time.
The surpise Group D seeds, who have a point to prove after some unflattering reaction to their exalted status, will have been buoyed by Iran's injury problems and indifferent recent form.
"This is the most important game. We know the game against Portugal will be really hard also so we really need to gain points in this game," said Iran skipper Ali Daei.
Mexico will hope to shrug off the absence of 'keeper Oswaldo Sanchez, whose father died in the week.
However a fourth-place finish in last year's Confederations Cup -- including a 1-0 win over Brazil -- and a 20-match unbeaten streak have instilled a strong sense of self-belief in Ricardo Lavolpe's squad.
"Mexico are very compact, aggressive and fast -- actually, they're excellent," said Lavolpe's opposite number Branko Ivankovic.
"Sometimes they're playing very boring, but very successful."
Key player is Barcelona rock Rafael Marquez, who will be looking to make amends for his red card in the knock-out defeat to the United States four years ago.
Mexico's all-time top-scorer Jared Borgetti, who totted up a world-best 14 goals in qualifying, will be hoping to send a message to club manager Sam Allardyce who left him languishing on the Bolton bench this season.
Meanwhile Iran, who have set their sights on making round two for the first time, look to have serious problems with several players either ruled out or recovering from injury.
With key attackers Ali Karimi and Mehdi Mahdavikia coming back from ankle and back trouble respectively, defender Sattar Zare twisted a knee in training and midfielder Fereydoon Zandi also looks likely to miss out after coming down with a fever.
However Iran, who have plundered a mine of information on their opponents, remain optimistic that the Asian giants could spring a surprise in their "most important game".
"Our coaching staff is analysing Mexico really well and every player is aware of the Mexican players and their style of the game. We know how to play against Mexico," said captain Daei.
"I think winning against Mexico is not unreachable. Mexico is a very good team but it's not unbeatable."
The match also has a political dimension with Iran, under fire for their president's comments about the Holocaust, playing in the former Nazi stronghold of Nuremberg.
Mexico won the two teams' only previous encounter, a friendly on June 9, 2001 which ended 2-1.